The present invention is of use in the field of hyperthermia for tumors such as cancers, and especially for those which are located in the depth of the body of a patient. Thus, broadly, the invention relates to an improved apparatus for high-frequency hyperthermia to be used in the above-described field.
Hyperthermia, which consists of heating an affected part to a temperature ranging from 43.degree. to 45.degree. C. for a period of time ranging from a little over 10 minutes to several tens of minutes, has turned out to be effective in recent years as one of the therapies for a cancer or other tumor, namely, as one of the treatments for a part affected by abnormal cellular tissues. The effectiveness of hyperthermia has been clinically recognized.
High-frequency heating, which takes advantage of dielectric loss in a high-frequency field, is being regarded as a promising way of applying hyperthermia to an affected part located in the depth of the body of a patient.
FIG. 1 shows a conventional method of heating an affected part 2 which is located in the depth of the body 1 of a patient. A pair of electrodes 3 and 4 are attached to the surface of the body 1 so as to interpose the affected part 2 therebetween. Then the electrodes 3 and 4 are connected to a high-frequency generator 5, and high-frequency energy is supplied across the electrodes 3 and 4 with matched impedance obtained by a matching transformer 6. Thus the portion of the body 1 interposed between the electrodes 3 and 4 undergoes dielectric heating. During this dielectric heating, normal cellular tissues contiguous to the abnormal cellular tissues are kept under control so as to be kept at a temperature ranging from 40.degree. to 42.degree. C. Then the temperature of the affected part 2 becomes higher by 2.degree. to 3.degree. C. than the temperature of the normal cellular tissues, because the affected part 2 is poorly vascularized and the vascular system in this part is in a condition of circulatory insufficiency. This means that only the abnormal cellular tissues constituting the affected part 2 are heated to a higher temperature ranging from 43.degree. to 45.degree. C. and thereby necrosis occurs in these tissues. It stands to reason, therefore, that one entertains great expectations of the therapeutic effect of hyperthermia on such an affected part as mentioned above.
The trouble is that there is a danger of inflicting a burn upon the surface of the body 1 to which the electrodes 3 and 4 are attached. In order to eliminate this danger, it is most common, as shown in FIG. 2, to interpose a pad between each electrode and the surface of the body 1. Cold water is put in circulation through the pads 7 and 8 so that the surface of the body 1 may be cooled thereby during the above-described high-frequency heating.
The electrodes 3 and 4 used in any of the above-described conventional apparatuses are of a disc type as shown in FIG. 3 and constitute a pair of parallel planar electrodes, each of which has an exactly or nearly round rim. High-frequency energy supplied across the electrodes of this type is inevitably dispersed as shown with a plurality of broken lines A in FIG. 4 which illustrate the distribution of lines of force. The dispersion extends over such a wide range that the high-frequency energy cannot be concentrated on the affected part 2. Thus the conventional apparatuses have a disadvantage that it is very difficult to heat only the affected part 2 to a sufficient degree, and a wide range of the normal cellular tissues contiguous to the affected part 2 is concurrently heated, not to say burnt.